Polymeric foams can be generally classified as either closed-cell foams or as open-cell foams. Open-cell foams can be used as a matrix to contain various liquids and gases. They are capable of various industrial applications such as, for example, use in wipes and diapers, as carriers and ion exchange resins. For some of these applications, it is desirable to have porous crosslinked polymer blocks which have a very low density and a high capacity of absorbing and retaining liquids. Such high absorption capacity, low density, porous polymer blocks can be prepared by polymerizing a specific type of water-in-oil emulsion known as high internal phase emulsion (HIPE) having relatively small amounts of a continuous oil phase and relatively greater amounts of an internal water phase.
Such high absorption capacity, low density foams are prepared in U.S. Pat. No. 4,522,953 by forming, in batches, high internal phase water-in-oil emulsions containing monomers in the continuous phase of the emulsion and polymerization initiators, and subsequently curing the emulsions at a temperature around 60.degree. C. for about 8 hours. Typically, to form the water-in-oil high internal phase emulsion, an aqueous solution of potassium persulfate initiator is added slowly to a container containing the stirred monomers and emulsifiers.
However, to produce larger quantities of the low density, porous, crosslinked, polymeric materials it is desirable to have a continuous mixing process to produce the emulsion. It is desirable to have a continuous mixing process with minimal process difficulties such as clogging of orifices or build-up of material on walls in the mixing vessel. Further, the resulting emulsions should be uniform and stable to produce reproducible foams. It is even desirable to avoid build-up of material on walls and mixer heads in the mixing vessel in a batch process.
It is therefore an object of the present invention to provide an improved mixing process to produce curable high internal phase emulsions.